Extra rain falling on continents partly offset the effect of melting ice caps last decade, data shows, with implications for coastal communities
By Megan Darby
Sea levels are rising. How fast is one of the most important and uncertain areas of climate science.
Melting ice in Greenland, Antarctica and mountain glaciers is the main driver. But the meltwater measurements don’t match up with the ocean levels recorded, suggesting other factors are at work.
A study published in journal Science on Thursday sheds light on the mystery. The gap can be explained by an increase in water stored in soils, aquifers and reservoirs, researchers found. Based on satellite data from 2002-14, that effect could have offset sea level rise by 20-25%.
Lead author John Reager, of NASA’s Jet Propulsion Laboratory, said: “Our study is the first one to show that natural variability could actually cause a gain in the water stored on land.
“What we have seen over the last decade is that natural variability – more rain falling on land – has slowed the rate of sea level rise.”
Over the period studied, sea levels rose by an average 2.4 millimetres a year. Without land-based hydrological effects, the expected rate would have been 3.2mm/yr.
What the researchers – hailing from universities in the US, Germany and Taiwan – don’t yet know is why more water was stored on land. That is a subject for future research, to try and predict how the effect could play out over the coming decades.
Greenhouse gas emissions are known to be altering rainfall patterns as well as pushing up temperatures. If that continues to result in more rain over the continents, it could offset the impacts of ice melt in the longer term. If, on the other hand, last decade’s measurements are part of a natural cycle, there could be a swing back to faster sea level rise.
“That is kind of the scary thing,” Reager told Climate Home. “The glaciers haven’t slowed down, they are still melting. It is possible this could reverse… and actually enhance sea level rise in future.”
Predicting the trend is critical for hundreds of millions of people living in coastal areas worldwide. Low-lying island states are on the front line, followed by megacities like Miami, Mumbai and Shanghai.